Variable rate flat spring arrangement

ABSTRACT

A suspension system for a vehicle is provided. The suspension system includes a first chassis rail extending longitudinally in an axial direction of the vehicle. The suspension system also includes a second chassis rail extending longitudinally in the axial direction of the vehicle. The suspension system further includes a transverse beam coupled to the first chassis rail and the second chassis rail. The suspension system yet further includes at least one leaf spring extending in a transverse direction of the vehicle, the at least one leaf spring having a spring rate that is actively variable. The suspension system also includes a fulcrum locator operatively coupled to the at least one leaf spring and to the transverse beam, the fulcrum locator in a sliding relationship with the at least leaf one spring.

CROSS REFERENCE TO RELATED APPLICATION

This patent application is a continuation application, and claimspriority to, U.S. patent application Ser. No. 15/574,031, filed Nov. 14,2017, which is a National Stage Application of PCT Publication No.PCT/US2016/032106, filed May 12, 2016, which claims priority to U.S.Provisional Patent Application Ser. No. 62/161,511, filed May 14, 2015,all of which are incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

This invention relates generally to variable rate flat springarrangements.

BACKGROUND

Leaf spring systems have for many years been used for the suspension ofwheeled vehicles. The central element of a leaf spring suspension systemfor a vehicle is termed a “semi-elliptical” spring configured as anarc-shaped length of spring steel having a substantially rectangularcross-section. At the center of the arc is provided an arrangement forcoupling to the axle of the vehicle. At the ends are provided couplerholes for attaching the spring to the vehicle body. For heavy vehicles,leaf springs are stacked on one another to form layers of springs ofdifferent lengths. Leaf springs are still used in heavy commercialvehicles and railway carriages. In the case of very heavy vehicles, leafsprings provide the advantage of spreading the load over a larger regionof the vehicle's chassis. A coil spring, on the other hand, willtransfer the load to a single point.

The well-known Hotchkiss drive, the name of which derives from theFrench automobile firm of Hotchkiss, employs a solid axle that iscoupled at its ends to the centers of respective semi-elliptical leafsprings. There are a number of problems with this form of drivearrangement. First, this drive system is characterized by high unsprungmass. Additionally, the use of a solid axle results in coupledleft/right wheel motion. During heavy cornering and fast acceleration,this known system suffers from vertical deflection and windup.

One effort to address the problems associated with the Hotchkiss systememploys a parallel leaf spring arrangement at each end of a solid axle.This known arrangement affords increased axle control, in the form ofreduced power hop. Other advantages of this arrangement include rollunder steer, auto load leveling and the gross vehicle weight, and noframe changes are required to convert from a Hotchkiss system. However,the parallel leaf spring arrangement employs a solid axle, and thereforedoes not provide the benefits of independent suspension. In addition,this arrangement is plagued with the disadvantage of high unsprung mass.

Accordingly, leaf spring suspension systems suffer from numerousdrawbacks that may be improved upon.

SUMMARY OF THE DISCLOSURE

According to one embodiment, a suspension system for a vehicle isprovided. The suspension system includes a first chassis rail extendinglongitudinally in an axial direction of the vehicle. The suspensionsystem also includes a second chassis rail extending longitudinally inthe axial direction of the vehicle. The suspension system furtherincludes a transverse beam coupled to the first chassis rail and thesecond chassis rail. The suspension system yet further includes at leastone leaf spring extending in a transverse direction of the vehicle, theat least one leaf spring having a spring rate that is actively variable.The suspension system also includes a fulcrum locator operativelycoupled to the at least one leaf spring and to the transverse beam, thefulcrum locator in a sliding relationship with the at least leaf onespring.

According to another embodiment, a variable rate spring arrangementincludes a flat spring extending from a first end to a second end. Thevariable rate spring arrangement also includes a fulcrum adaptoroperatively coupled to the flat spring and to a beam, the fulcrumadaptor moveable to modify an effective length of the spring to adjustthe overall stiffness of the spring.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a vehicle suspension system having atransverse spring arrangement according to one aspect;

FIG. 2 is a plan view of the vehicle suspension system of FIG. 1;

FIG. 3 is a side view of the vehicle suspension system of FIG. 1;

FIG. 4 is a front elevational view of the vehicle suspension system ofFIG. 1 with the transverse spring arrangement in a first position;

FIG. 5 is a front elevational view of the vehicle suspension system ofFIG. 1 with the transverse spring arrangement in a second position;

FIG. 6 is a perspective view partially illustrating the transverse leafspring arrangement;

FIG. 7 is a perspective view of the vehicle suspension system having atransverse spring arrangement according to another aspect of theinvention;

FIG. 8 is a plan view of the vehicle suspension system of FIG. 7;

FIG. 9 is a perspective view of an end of the transverse springarrangement of FIG. 7;

FIG. 10 is a perspective view of a fulcrum locator of the transversespring arrangement of FIG. 7;

FIG. 11 is a cross-sectional view of the fulcrum locator taken alongline A-A of FIG. 10; and

FIG. 12 is an enlarged view of a roller assembly of the fulcrum locator.

DETAILED DESCRIPTION

Referring to FIG. 1, illustrated is a vehicle suspension system 10having a chassis generally designated with numeral 12. The chassis 12includes a first chassis rail 14 and a second chassis rail 16 that arearranged substantially parallel to each other. The first and secondchassis rails 14, 16 are coupled to each another by at least one crossbrace, such as a first cross brace 18 and a second cross brace 20, asshown. A differential drive arrangement 22 is fixedly coupled to thechassis 12 and converts the rotary motion of a drive shaft (not shown)to substantially orthogonal rotary motion at half shafts 24 and 26. Eachof the half shafts 24, 26 include an associated pair of universal joints(not specifically designated) that are arranged to be proximal anddistal with respect to the differential drive arrangement 22. Thus, thehalf shafts 24, 26, each of which has an associated longitudinal axis,accommodate transaxial motion.

Half shafts 24, 26 are shown to be coupled at their distal ends torespective leaf springs 28 and 30. Referring to leaf spring 28, forexample, the leaf spring is, in this specific illustrative embodiment ofthe invention, operatively coupled proximate its ends to the chassis 12.It is to be appreciated that multiple leaf springs may be disposed in astacked arrangement. Additionally, although not illustrated, in someembodiments, a half leaf spring may be included and may be operativelycoupled to the chassis 12 proximate a first end of the half leaf springand to one of the half shafts 24, 26 proximate a second end of the halfleaf spring. In such embodiments, the half leaf spring(s) is located ina spaced manner from the leaf springs 28, 30, and may be located aboveor below the leaf springs 28, 30.

Referring now to FIGS. 2 and 3, with continued reference to FIG. 1, thevehicle suspension system 10 also includes a transverse springarrangement 40. As will be appreciated from the description herein, thetransverse spring arrangement 40 provides active, or variable, springrate change to work with the above-described leaf springs 28, 30 toadvantageously adapt to different loads applied to the vehiclesuspension system 10, achieve ride targets and improve vehicle dynamics.Typically, a leaf spring suspension system has predeterminedcharacteristics that are intended to accommodate certain loads, butvehicles may be subjected to different loads and the active spring ratechange capability of the vehicle suspension system 10 described hereinallows a user to modify the spring characteristics of the transversespring arrangement 40 to adapt to the specific load that the vehicle issubjected to. Therefore, the vehicle is leveled to maintain a desiredride height by varying the spring rate.

The transverse spring arrangement 40 includes at least one spring thatextends in a cross-car direction and substantially orthogonal to theleaf springs 28, 30. As noted, a single spring may be included, but aplurality of springs may be provided in some embodiments, such as theillustrated embodiment. In the illustrated embodiment, a first spring 42and a second spring 44 are included. The first spring 42 is operativelycoupled to the half shaft 24 proximate a first end 46 of the firstspring 42 and operatively coupled to the second chassis rail 16proximate a second end 48 of the first spring 42. The second spring 44is operatively coupled to the half shaft 26 proximate a first end 50 ofthe second spring 44 and operatively coupled to the first chassis rail14 proximate a second end 52 of the second spring 44. The aforementionedcoupling arrangement of the first and second springs 42, 44 therebycouples the half-shafts (e.g., axles) to the chassis 12. As shown inFIG. 6, the ends of the springs 42, 44 that are operatively coupled tothe chassis 12 include shackles to reduce or prevent side-to-sideshifting of the vehicle during operation, particularly during turningmaneuvers.

The above-described springs, e.g., leaf springs 28, 30 and the first andsecond springs 42, 44 may be referred to as “semi-elliptical” springsconfigured as arc-shaped length segments. In some embodiments, thesprings are formed of spring steel having a substantially rectangularcross-section. In other embodiments, a composite material may be used.However, alternative materials and geometries are contemplated.

To achieve the active rate control of the above-described first andsecond springs 42, 44, a fulcrum location of each of the springs 42, 44is modified with a fulcrum adaptor 54. For purposes of discussion, onlymodification of the fulcrum location of the first spring 42 will bedescribed in detail, but it is to be understood that both springs areassociated with a respective fulcrum adaptor. In the illustratedembodiment, the fulcrum adaptor 54 comprises a clamping arrangement 54that is operatively coupled to a transverse beam 56 that extends in across-car direction and is fixed to the first chassis rail 14 and thesecond chassis rail 16 proximate respective ends of the transverse beam56. The clamping arrangement 54 clamps the first spring 42 to maintainthe fulcrum location at the clamped location. The clamping arrangement54 is coupled to both the transverse beam 56 and the first spring 42 ina manner that allows the clamping arrangement 54 to slide relative tothese components. The sliding relationship facilitates modification ofthe fulcrum location to adjust the spring rate characteristic. Thisimpacts the overall suspension dynamics and ride characteristics, aswell as provides the desired extent of leveling of the vehicle during acurrently applied load.

Referring to FIGS. 4 and 5, the vehicle suspension system 10 isillustrated in distinct positions. In particular, FIG. 4 shows thesystem 10 and, more particularly, the transverse spring arrangement 40in a first position, while FIG. 5 illustrates the springs of thetransverse spring arrangement 40 in a second position. As discussedabove, the actively controlled characteristics (e.g., spring rate) ofthe springs 42, 44 of the transverse spring arrangement 40 vary theresponse characteristics of the overall vehicle suspension system 10.

Referring now to FIGS. 7-12, another embodiment of the vehiclesuspension system 10 is illustrated. The illustrated embodiment includesanother embodiment of the fulcrum adaptor 54 that is configured toactively modify the spring rate of the first and second springs 42, 44.The fulcrum adaptor 54 comprises a roller assembly 60 that is displacedalong the first and second springs 42, 44 via a linear screw actuationassembly 62.

The linear screw actuation assembly 62 is fixed to the chassis 12 at arespective chassis rail, as best shown in FIGS. 7 and 9. A threadedshaft 64 extends in a transverse direction and through the chassis railinto a drive socket 68 that is coupled to the chassis rail. At anopposing end of the threaded shaft 64, coupling is made to a bearing 70that is coupled to a cross member 72. It is to be appreciated that thebearing associated with the first and second springs 42, 44 are coupledto a single cross member or to respective cross members.

The roller assembly 60 includes at least one roller 74 directly incontact with the springs 42, 44 and is coupled to a roller bracket 76.The roller bracket 76 is coupled to a threaded slider block 78 that isdirectly coupled to the threaded shaft 64, thereby indirectly couplingthe roller 74 to the threaded shaft 64 for movement therealong. One ormore stopping features, such as a retaining clip 80 may be positioned onthe threaded shaft 64 to retain the roller assembly within a desiredboundary along the length of the threaded shaft 64.

Regardless of the precise type of fulcrum adaptor 54 employed, theadaptor may be controlled either manually or in an automated manner. Forexample, manual control of the transverse spring arrangement 40 may becarried out by a hand crank that is coupled to an input of thearrangement. Automated control of the fulcrum adaptor 54 may be madewith a control system that is located onboard the vehicle in someembodiments and remotely in other embodiments. Remote control may bedone with a wireless device, for example.

The embodiments described herein define active rate control of a springor beam. This may be referred to as “active rate beam theory,” whichfacilitates controlling system dynamics in an advantageous manner. Asdescribed above, this is done by manipulating the fulcrum location toalter the moment applied to the beam or spring. Although described abovein terms of a transverse spring arrangement, it is to be understood thatactive rate beam theory may be applied to differently oriented springarrangements. For example, the fulcrum adaptor 54 may be operativelycoupled to a longitudinally extending spring, such as leaf spring 28 or30, or to a longitudinally extending spring located above or below leafspring 28 and/or 30. Additionally, the fulcrum adaptor 54 may beoperatively coupled to a spring that is part of a triangulatedarrangement and that extends in a diagonal manner. Therefore, thefulcrum adaptor 54 may be applied to a longitudinally extending springarrangement, a transverse spring arrangement, and/or to a springarrangement that is oriented at any diagonal angle relative to thetransverse and longitudinal directions. The active rate beam theory maybe applied to a single spring arrangement or any combination of theabove-specified arrangements.

The embodiments described herein may be employed in any type ofsuspension arrangement. For example, a control arm suspension maybenefit from the active rate control described herein. In such anembodiment, an upper and/or lower arm may benefit from active ratecontrol, such as a transverse configuration of the upper and/or lowerarm. Also, a rear twist axle may benefit from the embodiments describedherein.

It is to be appreciated that the features and advantages of “active ratebeam theory,” as described above, may be applied to any springarrangement, particularly flat spring arrangements. Therefore, thefeatures related to controlling the spring characteristics (e.g.,stiffness) by manipulating an effective length of the spring may beapplied to any vehicle or non-vehicle application having a springarrangement.

Although the invention has been described in terms of specificembodiments and applications, persons skilled in the art may, in lightof this teaching, generate additional embodiments without exceeding thescope or departing from the spirit of the invention described herein.Accordingly, it is to be understood that the drawing and description inthis disclosure are proffered to facilitate comprehension of theinvention, and should not be construed to limit the scope thereof

Having thus described the invention, it is claimed:
 1. A suspensionsystem for a vehicle, the suspension system comprising: a first chassisrail extending longitudinally in an axial direction of the vehicle; asecond chassis rail extending longitudinally in the axial direction ofthe vehicle; a transverse beam coupled to the first chassis rail and thesecond chassis rail; at least one leaf spring extending in a transversedirection of the vehicle, the at least one leaf spring having a springrate that is actively variable; and a fulcrum locator operativelycoupled to the at least one leaf spring and to the transverse beam, thefulcrum locator in a sliding relationship with the at least leaf onespring.
 2. The suspension system of claim 1, wherein the fulcrum locatorcomprises a clamping element.
 3. The suspension system of claim 1,further comprising: a first leaf spring element extending longitudinallyin the axial direction of the vehicle, the first leaf spring elementoperatively coupled proximate ends thereof to the first chassis rail andat an intermediate location to an axle assembly of the vehicle; and asecond leaf spring element extending longitudinally in the axialdirection of the vehicle, the second leaf spring element operativelycoupled proximate ends thereof to the second chassis rail and at anintermediate location to the axle assembly of the vehicle.
 4. Thesuspension system of claim 2, wherein the fulcrum locator comprises aroller assembly driven by a linear screw actuator.
 5. The suspensionsystem of claim 1, wherein the at least one leaf spring is operativelycoupled to the chassis rail and to the axle.
 6. The suspension system ofclaim 1, wherein the at least one leaf spring comprises a firsttransverse leaf spring and a second transverse leaf spring.
 7. Avariable rate spring arrangement comprising: a flat spring extendingfrom a first end to a second end; and a fulcrum adaptor operativelycoupled to the flat spring and to a beam, the fulcrum adaptor moveableto modify an effective length of the spring to adjust the overallstiffness of the spring.
 8. The suspension system of claim 7, whereinthe fulcrum adaptor is operatively coupled to the flat spring andslidable relative thereto.
 9. The suspension system of claim 7, whereinthe fulcrum adaptor comprises a clamping element.